This invention relates to a developer material coating apparatus for coating a support member such as a plain paper with granular developer material, and more particularly to a developer material coating apparatus having a developer material removing unit.
There has been recently utilized a color copying machine in which a color image is formed on a support member such as plain paper using granular developer material and a microcapsule sheet. A color image forming process of this type of color copying machine is as follows. A developer sheet is beforehand formed by coating the developer material on the support member such as plain paper, and the microcapsule sheet is exposed through an original to light to form a latent image on the microcapsule sheet. The microcapsule sheet having the latent image thereon and the developer sheet comprising the support member coated with the developer material are fed to a pressure-developing unit while contacted with each other under pressure. In the pressure-developing unit, the microcapsule sheet and the developer sheet are subjected to a pressure-developing process to develop the latent image on the microcapsule sheet into a visible color image on the developer sheet. Thereafter, the developer sheet having the visible color image thereon is fed to a heat-fixing unit to thermally fix the visible color image on the developer sheet. The developer material is formed of , for example, acid clay, binder and so on, and thus the developer sheet may comprise the support member coated with the developer material formed of the acid clay, the binder and so on.
As described above, this type of color copying machine requires a process for coating the developer material on the support member such as plain paper, and thus a coating apparatus therefor. As a coating apparatus, there has been conventionally used a coating apparatus in which the developer material on the support member is charged with triboelectrification and then is electrostatically coated on the support member.
FIG. 1 shows a conventional coating apparatus for coating the developer material on the support member such as plain paper. This coating apparatus comprises, for example, a support member feeding unit for feeding the support member to a developer material coating region in which the support member is electrostatically coated with the developer material and then discharging the support member coated with the developer material to an outside of the coating apparatus, and a developer material coating unit for triboelectrically charging the developer material and electrostatically supplying the charged developer material to the support member which has been fed to the developer material coating region.
The developer material coating unit comprises a tank for accommodating the developer material S therein, a carry roller 52 for carrying the developer material thereon and a supply roller 51 for triboelectrically charging the developer material in cooperation with the carry roller 52 and supplying the charged developer material to the carry roller 52. The carry roller 52 is grounded as shown in FIG. 1. The carry roller 52 and the supply roller 51 are rotatably contacted with each other at the peripheral surfaces thereof, and the developer material S is triboelectrically charged at a predetermined polarity (positively or negatively ) at the contacted surfaces of the rollers 51 and 52 through a friction between the surface of the carry roller 52 and the developer material S. The charged developer material S is attached to peripheral surface of the carry roller 52 and then is fed to the developer material coating region while carried on the carry roller.
The support member feeding unit comprises a counter electrode roller 53, which is supplied with a voltage having the opposite polarity to that of the charged developer material from a D.C. power source, a pair of guide rollers 55 provided away from the counter roller 53 and a carry belt 54 such as an endless belt for feeding the support member to the developer material coating region while carrying the support member P thereon and discharging the support member coated with the developer material (developer sheet) to the outside of the coating apparatus, the carry belt 54 being suspended among the counter roller 53 and the guide rollers 55. In FIG. 1, since the developer material S is positively charged, the counter electrode roller 53 is supplied with a negative voltage.
The support member P carried on the carry belt 54 is fed to the developer material coating region by the rotation of the counter roller 53 and the guide rollers 55. The positively-charged developer material S on the carry roller 52 is electrostatically attracted toward the counter electrode roller 53 due to an electric field which is caused between the counter roller 53 having a positive potential and the grounded carry roller 52. That is, particles of the positively-charged developer material S is electrostatically attracted (flight) toward the counter electrode roller 53 in the developer material coating region where the counter roller 53 and the carry roller 52 are confronted to each other, and attach to the support member P to form a developer material layer m on the support member P, that is, a developer sheet.
In the conventional developer material coating apparatus thus constructed, the developer material S, which has been electrostatically attracted toward to the counter electrode roller, is liable to be attached to any portion of carry belt 54, for example, the surface thereof located between the neighboring support members which are successively fed to the carry roller. Further, if the carry belt 54 has a hole in the surface thereof and a damaged portion therein, then the developer material is also attached to the surface of the counter electrode roller 53 through the hole and so on. Still further, if the counter electrode roller 53 is so designed as to have a longer width than the carry belt 54, then the developer material S is also attached to the surface of the counter electrode roller 53 through the side portion of the carry belt 54. Once the developer material S is attached to the surfaces of the carry belt 24 and the counter electrode roller 53, it is very difficult to remove the developer material S from the carry belt 24 and the counter electrode roller 53 because of nonconductivity of the developer material S. Accordingly, the developer material S is liable to be stacked on the surfaces of the carry belt 24 and the counter electrode roller 53. The stacking of the developer material S on the carry belt and the counter electrode roller 53 prevents a gap between the support member P and at least one of the carry belt and the counter electrode roller 53 from having a regular interval (that is, a gap interval between the counter electrode roller 53 and the support member is not constant over the surface of the support member P) and therefore the developer material S is not uniformly coated over the surface of the support member P. When the microcapsule sheet and the support member coated unevenly with the developer material on the surface thereof (that is, the support member coated with a developer material layer having an uneven thickness) are pressure-developed in the pressure-developing unit while contacted with each other, an image having uneven image density is obtained.